About 2,500 people had attended the rave party in an unused warehouse in Lieuron, near Rennes, and some clashed with police on Saturday, police said.
Interior Minister Gerald Darmanin said on Twitter that party-goers were issued with fines as they left the site and organisers were being identified and would be prosecuted.
The Ille-et-Vilaine prefecture said on Twitter 450 fines had been handed out for attending an illegal party, breaking curfew and not wearing masks. Local health authorities urged party-goers to self-isolate for seven days.
Prosecutors in Rennes have opened a probe into the illegal organisation of a musical event and violence against persons of authority, the prefecture said on Saturday after the clashes.
A police car caught fire and three others were damaged, the prefecture said. Party-goers threw bottles and rocks at police, and several officers suffered minor injuries.
With the highest number of COVID-19 cases in western Europe, France is stepping up coronavirus restrictions, imposing an earlier curfew in 15 northeastern and southeastern departments from Saturday, starting at 6 p.m. instead of 8 p.m.
France has already had two national lockdowns since the outbreak started and the latest was eased in mid-December, but restaurants and bars are off limits for now and it is not clear when they might re-open.